Method for electrochemical modification of liquid streams

ABSTRACT

A method for electrochemical modification of liquid streams employing an electrolytic cell which utilizes an oxidation site defined by an anode, an anode compartment comprising liquid electrolyte anolyte where oxidation is effected, a cathode compartment comprising liquid electrolyte catholyte where reduction is effected, a cathode comprising conducting cathode particulates forming a cathode particulates bed and a current feeder device in at least intermittent contact with said cathode particulates where the cathode particulates are in motion and the particulates motion is substantially independent of bulk electrolyte flow, a separator which confines the cathode particulates to the cathode compartment, constrains electrolyte flow through the cathode particulates bed and permits ionic conduction of current between the anode and cathode, a cathode particulates conveyance system that manipulates cathode particulates motion. A separate system circulates the liquid undergoing modification through the electrolytic cell. An unidirectional current driving system drives unidirectional electric current supported by the liquid streams from the anode through the anolyte and the separator and into the catholyte and to the cathode particulates and to the current feeder device during the contact between the cathode particulates and the current feeder device.

RELATED APPLICATIONS

This application is a divisional application of the U.S. patentapplication Ser. No. 11/623,658 filed on 16 Jan. 2007, which isincorporated here by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

Parts of this invention were conceptualized developed and reduced topractice using US government funding under National Institutes of Health(NIH) Small Business Innovation Research (SBIR) grant 1 R43ES013622-01A1. The US government has certain rights in this invention.

FIELD OF THE INVENTION

The invention relates to an apparatus and a method for modification ofliquid streams which contain organic and/or inorganic impurities. Moreprecisely, the invention is concerned with an electrolytic celltechnology with potentials to achieve reduction of contaminants commonlyfound in liquid waste streams and economically feasible extraction ofselected dissolved contaminants for commercial applications.

BACKGROUND OF THE INVENTION

Contamination of liquid streams with various organic and inorganicpollutants is a serious environmental problem affecting the quality ofthe global environment and represents a significant threat to humanhealth and safety. Substantial heavy metal contamination of aquaticenvironments arises from commercial mining and metal extractionprocesses, surfaces modification and protection processes, or communaland industrial waste sites resulting from a variety of active or defunctindustrial fabrication and manufacturing activities. Similarly,significant organic water pollutants, like aliphatic, aromatic, orhalogenated hydrocarbons and phenols, are frequently associated withoil, gas, and coal exploration, extraction and refining, chemicalindustry, or large-scale farming and food processing.

In addition to potential for significant environmental damage, pollutedliquid streams represent sources of desirable raw materials like heavymetals and metal oxides. For example, the Berkeley Mine Pit in Butte,Mont. alone represents an estimated 30 billion gallons of acid minedrainage which contains ˜180 ppm of copper along with other metals andthus could yield up to 22,000 tons of pure copper by use of a smalltreatment facility.

The prevailing method of removal of heavy metal ions from liquidsolutions is chemical precipitation. This process is burdened bycomplexity, high cost, clear preference for extremely large facilitiesand high-volume operations, and little selectivity towards targeting andseparating specific metallic pollutants. One fundamental disadvantage isthe resulting byproduct of considerable volumes of heavy sludge which istoxic due to contamination with a mixture of toxic heavy metals. Thesludge mandates further processing and costly long term disposal as ahighly toxic waste. Many similar disadvantages burden alternative heavyion removal methods that may incorporate: filtration, ion exchange, foamgeneration and separation, reverse osmosis, or combinations of listedprocesses.

Modification of polluted liquid streams can be accomplished efficientlyusing electrochemical processes. Electrochemical methods of reduction ofmetal ions or oxidation of organic pollutants do not suffer fromdescribed disadvantages of complexity, strong preference for large scaleoperations, or toxic byproducts. Advanced electrochemical methods likeMoving Bed Electrode (MBE) electrolytic technology in various forms isrelatively efficient even in the cases of comparatively low contaminantconcentrations of about 1000 ppm.

Liquid stream modification using a Spouted Electrode Technology (SET)variant of the moving bed cell is well-known to prior art. U.S. Pat. No.4,272,333 to Scot et al. discloses a method of moving bed electrolysiswhere motion of a particulate bed electrode; imposed by the circulationof electrolyte, prevents electrode particulates aggregation andmaintains at least intermittent contacts between the moving particulatesbed electrode and current feeder. Scot et al. report copper, zinc,cobalt, and manganese ions reduction from electrolytes with varying pHvalues.

U.S. Pat. No. 5,565,107 to Campen et al. discloses a process ofelectrochemical purification of “streams which contain organic and/orinorganic impurities”. The disclosed process utilizes a reactor with “awater-containing reaction zone which comprises providing a packed bed ofactivated carbon, applying an electrochemical potential across saidpacked bed and simultaneously feeding a reactant selected from the groupconsisting of ozone and hydrogen to said packed bed.”

Efficient electrowinning of zinc in an electrowinning cell using“moving” or “moving packed bed” SET electrode is disclosed in the U.S.Pat. No. 5,635,051 to Salas-Morales et al. from predominantly acidicelectrolytes. Related U.S. Pat. No. 5,958,210 to Siu et al. discloseselectrowinning of zinc in an SET electrowinning cell from alkalineelectrolytes. Both patents also disclose an industrial scaleeight-draft-tubes parallel electrowinning cell structure shown in sideelevation in corresponding FIG. 2.

Spiegel et al. in the U.S. Pat. No. 6,298,996 report purification ofmetal and toxic organic compounds from polluted aqueous waste streamsusing “an advanced electrolytic cell technology employing a dynamicspouted electrode” SET device. Spiegel et al. also disclose afour-independent-cells device in which electrolyte is pumped in aparallel manner into the cells and returned to the reservoir.

A simplified schematic side view cross-section of a SET cell of priorart is given in FIG. 1. A typical SET cell consists of one or moreanodes 10 coupled to one or more high surface area cathodes 20 in theform of spouted particulates bed, separated by a distance. Catholyteflow 30, driven by an external catholyte pumping station 40, is directedthrough the high surface cathode 20 to achieve vigorous particulates bedconvection needed for high degree of electrode utilization.Unidirectional current is fed into the cell via anode current feed 50(+)and out via cathode current feeder device 90 and cathode current feed50(−). The cell illustrated in the FIG. 1. is a simple planarconfiguration comprising cathode cell chamber 60 and anode cell chamber70 separated by a separator (porous membrane) 80 which directs bulkelectrolyte flow 30 while maintaining intimate electrochemical contactby ion transport (selective and/or non-selective) between the separatedcathode 20 and anode 10. Depending upon the state of control valvesystem 85 the cell can operate in a batch mode processing the fluidcontained in the reservoir 97, or in a flow-through mode modifyingliquid streams delivered by external pipelines 95. A mode of operationcreated by any combination of the flow-trough and batch modes can beachieved if desired in accordance with application specific requirementsand circumstances.

An important common feature of the prior art SET devices and processesis the fact that actuation of the electrode bed is achieved by vigorouscirculation of electrolytes generally achieved by strong pumping actionof various external pumping systems. This feature, clearly motivated bysimplicity of the mechanical design, is inherently suboptimal becausethe achievement of optimal liquid stream flow rate is sacrificed to therequirement for vigorous spouted bed mixing and circulation. The systemsof the prior art frequently comprise relatively powerful pumpingstations, like one denoted by the reference numeral 10 (correspondingreference numeral 31 in the U.S. Pat. Nos. 5,635,051 and 5,958,210).

In addition to higher capital cost and higher energy consumption,pumping stations scaled up to sufficiently mix and circulateparticulates beds in SET cells additionally burden the overallefficiency of the liquid stream modification processes by limiting thereactor residence time of treated liquid stream volumes. The devices andmethods in accordance with the present invention are designed toessentially decouple the fluid flow and motions of the SET. This novelcharacteristic of the devices designed in accordance with the presentinvention allows for independent optimization of the SET motionsnecessary for improved overall efficiency of the liquid streammodification processes and efficient electrolysis, prevention ofparticulates aggregation, and dendrite formation, and treated fluidcirculation optimized for sufficient reactor resident time necessary forefficient liquid stream treatment even in cases of streams comprisingsub 100 ppm concentrations of treatment target materials.

SUMMARY OF THE INVENTION

The present invention considers an apparatus and a method forelectrochemical modification of liquid streams employing an electrolyticcell which comprises a cathode comprising conducting cathodeparticulates forming a cathode particulates bed, and a current feederdevice in at least intermittent contact with the cathode particulates.The cathode particulates are in motion and the particulates motion issubstantially independent of bulk electrolyte flow. A separator confinesthe cathode particulates to the cathode compartment, constrains bulkelectrolyte flow through the particulate cathode bed and permits ionicconduction of current between the anode and cathode. A separate cathodeparticulates conveyance system drives and manipulates cathodeparticulates motion.

The method of present invention includes: circulating liquid streamundergoing modification through said electrolytic cell, activatingcathode particulates conveyance system to form the moving cathodeparticulates bed immersed in the catholyte and transporting the cathodeparticles bed substantially independently from catholyte circulation,bringing cathode particulates bed in at least intermittent contact withthe current feeder device, energizing the system for conductingunidirectional electric current to drive current supported by the liquidstreams from the anode through the anolyte and the separator and intothe catholyte and to the cathode particulates and to the current feederdevice during the contact between the cathode particulates and thecurrent feeder device and sustaining the achieved current conductionlong enough to electrochemically react at least detectable quantities oftargeted constituents of liquid streams undergoing modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. is a schematic cross-sectional side view of a spoutedelectrolytic technology (SET) moving bed cell in accordance with priorart.

FIG. 2. is a schematic cross-sectional side view of a moving bedelectrolytic cell in accordance with the present invention.

FIG. 3. is a schematic cross-sectional front view comparing theelectrolyte flow and cathode particulates convection of an electrolyticcell in accordance with prior art and an electrolytic cell in accordancewith the present invention.

FIG. 4. is a schematic cross-sectional top view of a cylindricalelectrolytic cell in accordance with an embodiment of the presentinvention.

FIG. 5. is a schematic cross-sectional side view of an electrolytic cellwith a mechanical cathode particulates conveyance system comprising ascrew type conveyor in accordance with the preferred embodiment of thepresent invention.

FIG. 6. is a schematic cross-sectional side view of an electrolytic cellwith a mechanical cathode particulates conveyance system in accordancewith a different embodiment of the present invention.

FIG. 7. is a schematic cross-sectional side and top views of an cathodehalfcell with a magnetic cathode particulates conveyance system inaccordance with an additional embodiment of the present invention.

FIG. 8. is a schematic cross-sectional side view of an electrolytic cellwith systems for removal of products of electrochemical reactions inaccordance with the present invention.

FIG. 9. is a graphic representation of unidirectional current profilesschematic in accordance with the present invention.

FIG. 10. is a graphic representation of copper concentration versus timeduring the batch operation of the proffered embodiment cell.

Like reference numerals identify like parts throughout the drawings.

DETAILED DESCRIPTION OF THE INVENTION

A simplified schematic side view cross-section of the electrolytic cellof in accordance with current invention is given in FIG. 2. Theprinciple difference of the cell depicted in FIG. 2 is the addition of aseparate cathode particulates conveyance system 100 that manipulatescathode particulates motion substantially independently from thecatholyte flow 30. In contrast with the prior art pumping systemssimilar to one depicted in FIG. 1, the external catholyte pumpingstation 110 of current invention in FIG. 2 needs only provide relativelyslow catholyte flow 30 and can be readily adjusted and directedthroughout the cathode particles bed for easy process optimizationwithout significantly altering the particles bed motion. The pumpingstation 110 of current invention requires relatively lower pumpingcapacity resulting in smaller size, lower cost, and, most importantly,lower electric energy consumption and the ability to readily manipulateand control the catholyte flow rate and pattern with the moving cathodeparticles bed.

The principle difference in the catholyte flow 30 and cathodeparticulates convection 120 between the prior art cells with spoutingtubes 300(“draft tube 16” in U.S. Pat. Nos. 5,635,051 and 5,958,210) andthe electrolytic cell with a separate cathode particulates conveyancesystem 100 of current invention is given schematically in FIG. 3 a andFIG. 3 b. While the spouting tube 300 of a prior art cell inducesvigorous catholyte flow 30, causing circulation of excessive volumes ofcatholyte in order to indirectly produce sufficient cathode particulatesconvection 120, the particulates conveyance system transfer momentumpredominantly directly to the cathode particulates, contributing onlymarginally to the catholyte flow 30. The opportunity for independentoptimization of the catholyte flow 30 and catholyte ions resident timeleads to the extension of the parameter space of efficient andeconomically feasible operations of cells in accordance with the presentinvention to the concentration ranges well below 100 ppm of target ionconcentrations.

A variety of electroactive solutions comprising solvent, electrolyte,and possibly supporting electrolytes meeting chemical andelectrochemical potential window stability criteria will work with thepresent technology. The anolyte and catholyte can be the same ordifferent depending on the targeted application. Specifically, initialdemonstrative work for reducing the technology to practice employed asingle shared electrolyte for anolyte and catholyte. A synthetic acidmine drainage solution was prepared using water as the solvent as thisrepresents the most common solvent.

The ionically conducting species of the electrolyte were provided byadded ionizing compounds which dissolved in the solvent. While aplethora of suitably soluble, conductive, and electrochemically stablecompounds exist, initial work utilized copper sulfate pentahydrate. Herethe sulfate anion was stable in the electrochemical potential window ofinterest and the cupric ion provided the target species forelectrochemical reduction at the cathode. Water oxidation to generateoxygen was targeted at the anode as the complimentary oxidation reactionto the targeted reduction process.

Several supporting electrolytes were also added to better mimic thecomposition of acid mine drainage. Sulfuric acid was added to lower thesolution pH while sodium sulfate was added to increase the sulfateconcentration to levels typical of actual acid mine drainage. As thesulfate and sodium are inactive in the potential window of interest,they act simply as supporting electrolytes. Similarly, while protons canbe reduced to hydrogen at the cathode, except under mass transferlimitations, cupric ion reduction will dominate and the dissolvedprotons will effectively serve as supporting electrolyte ions.

An embodiment of electrolytic cells in accordance with the presentinvention possessing cylindrical symmetry is shown in FIG. 4. The cellsin FIG. 4 comprise anode 10 and cathode 20 in the form of coaxialcylinders. In FIG. 4 a cylindrical spouted bed cathode 20 encompassesthe cathode particulates conveyance system 100, while both areencompassed by the separator 80 and cylindrical anode 10. In the highestcylindrical symmetry configuration, the cathode particulates conveyancesystem 100, the cathode current feeder device 90, the spouted bedcathode 20, the separator 90, and the anode 10 comprise a system ofcylindrical tubes filled by the electrolyte.

In FIG. 4 b the cylindrical anode 10 in the form of conductive rod isencompassed by the separator 80 and spouted bed cathode 20 sharing acommon vertical axis of cylindrical symmetry. The cathode particulatesconveyance system 100 is distributed throughout the cathode particlesbed in order to provide substantially uniform actuation of the cathodebed particulates. It is obvious to the practitioners of the art ofelectrochemistry that systems with somewhat different geometries thatpreserve similar topology as the cells given schematically in FIG. 2 andFIG. 4 represent an apparatus in accordance with the present inventionand will function in the manner in accordance with the claims of thepresent application.

It is frequently desirable, for an efficient and consistent function ofan electrolytic cell, that anode 10 does not lose electrode material tothe oxidation reaction on anode surfaces inseparable from the properfunction of any electrolytic cell. Anodes which substantially preservetheir original shape and relationship with the other components ofelectrolytic cells are known in the art to be geometrically stable.

Many geometrically stable anodes comprising platinized titanium, niobiumcoated copper, and oxide coated conductive substrate or combination ofthis and other refractory materials are known to the practitioners. Theanodes can incorporate relatively smooth active surfaces, or poroussurfaces that benefit from the additional surface area introduced by theadded pores.

In addition, the anode materials comprising lead and lead alloys can beconsider geometrically stabile over the electrochemical-process-relevantperiods of time in spite the fact that the anode surfaces exhibit verygradual corrosion. The corrosion process of the lead comprising anodesurfaces is especially slow and relatively uniform in processes relatedto electrochemical modifications of liquid streams containing the targetmaterials at dilute concentrations. For the purpose of the presentinvention the anodes comprising lead and lead alloys are included in theset of geometrically stabile anodes.

Commercially available anodes like the Eltech Systems Corporation EC-600dimensionally stable anode (DSA) comprised of tantalum doped iridiumoxide coatings on titanium substrates and optimized for oxygengeneration were successfully tested during the development of methodsand apparatus of the present invention.

Separators 80 perform confinement of the cathode particulates to thecathode compartment and constrain of electrolyte flow through thecathode particulates bed. The separator 80 is in form of membrane,diaphragm, or other permeable mechanical barrier material that permitsionic conduction of current between the anode and the cathode. Thepreferred separator materials do not participate in electrochemicalreactions of the cell, but the listed separator functions can be inprinciple performed by separators constructed from materials thatsupport the ionic current conduction by ion-exchange reactions on theseparator surfaces. The cells with particulates motion substantiallyindependent of bulk electrolyte flow, utilizing ion-exchange separatormembranes are recognized as specific embodiments of the currentinvention.

Separators 80 with surfaces that define planes are depicted in FIG. 2,while separators 80 with cylindrically-symmetric surfaces that definetubes are depicted in FIG. 4. Because of the influence of gravity on thecathode particulates convection, the preferred orientation of separatorsurfaces that define the plane is with the plane parallel to thevertical axis, while the preferred orientation of thecylindrically-symmetric separator surfaces is with the cylindrical axisparallel to the vertical axis. It is recognized that any non-horizontalorientation, with the separator surfaces planes and/or cylindrical axisform non-zero angles with horizontal planes, will function in accordancewith the present invention.

The preferred cathode particulates conveyance system 100 thatmanipulates cathode particulates motion is a mechanical system in thegeneral form of a screw type conveyor 500(“Archimedes screw”) shownschematically in FIG. 5. The cathode particulates convection is achievedby a direct action on the cathode particulates by a helicoidal surfacethat rotates in preferred sense 510 around the axis 520 powered by anexternal driver. The diameter of the system, the helicoil pitch andflute to flute separation, rotational velocity, and the driving powershould be designed for an operation optimal for the particularapplication. The preferred speed of rotation for the test device usedfor the development of this invention is in the range from 10 RPM to 500RPM.

A different embodiment of the cathode particulates conveyance system 100is shown in cross-sections in FIG. 6. where the mechanical cathodeparticulates conveyance system comprises a moving bucket 620 typeconveyor 600. The moving bucket 620 type conveyor 600 comprises a belt650 guided and actuated to circulate by the actuators 640. The beltcarries buckets 620 positioned periodically along the belt. Thecirculation of the belt and the direct action of the buckets upon thecathode particulates causes desired cathode particulates convection 120.Positioning of the particulates guide 630 in the proximity of the locusof separation of cathode particulates from the conveyer 600 facilitatesthe efficiency of the cathode particle convection.

A different variation on the moving bucket type mechanical conveyer 600is a moving belt 650 type conveyer where bucket 620 are omitted and themomentum is predominantly transferred to the cathode particulates byfrictional forces between the belt 650 and the particulates.

In the embodiment when at least a fraction of the cathode particulatescomprise at least a portion of their mass in the form of ferromagneticmaterial, significant interaction between the cathode particulates andthe cathode particulates conveyance system 100 can be achieved when atleast one permanent magnet is attached to the conveyer belt 650 in suchmanner that significant portion of the magnetic field penetrates thecathode chamber 60. In this embodiment, the particles guide 630 needs tobe positioned in the proximity of the conveyer at a preferable clearancesmaller than the particulates' diameter in order to achieve efficientseparation of magnetized particulates from the proximal permanentmagnet.

A variation of this embodiment where the conveyer belt materialcomprises permanently magnetized portions to produce the cathode chamberpenetrating magnetic field is recognized to be in the scope of thepresent invention. It is also recognized that many mechanical andmagnetic cathode particulates conveyance systems can operate withsynergy. Combinations of mechanical cathode particulates conveyancesubsystems and magnetic cathode particulates conveyance systems can bedesirable to drive sufficient cathode particulates conveyance either inmodular liquid streams modification operations or as parts andsubsystems of integrated electrolytic cells.

A different embodiment utilizing magnetic interaction between thecathode particulates and the cathode particulates conveyance system usestraveling magnetic fields. Sources magnetic fields comprise coils withloops of electric conductors each arranged to generate magnetic fieldssymmetric with respect to prospective horizontal planes of symmetry whenloops of electrical conductors are energized by at least one externalsource of electric current. This external source of electric currentflowing through electromagnets' loops of electric conductors isgenerally independent and separate from the system for conductingunidirectional electric current supported by the liquid streams from theanode through the anolyte and the separator and into the catholyte andto the cathode particulates and to the current feeder device during thecontact between the cathode particulates and the current feeder device.

A schematic rendering of the embodiment shown in FIG. 7 utilizesspouting tube 300 and a set of electromagnets 700 with coils 710,ferromagnetic core 720, and ferromagnetic pole pieces 730. Whenenergized by the external source of electric current modulated in timeto create magnetic pulses traveling with a velocity 740 with non-zerovertical component. The magnetic pulse is formed by combinedtime-variable magnetic fields produced by the coils. The fields arecharacterized by a volume of high magnetic induction B 750 thatcontinuously transfers toward the upper end of the cathode compartment60 for the duration of the magnetic pulse.

The cathode particulates are chosen to have at least partiallyconductive surfaces necessary to achieve at least intermittent contactbetween particulates and the current feeder device. When the travelingmagnetic inductance 750 intersects the surfaces of the proximal cathodeparticulates it induces eddy currents in the particulates that interactsrepulsively with the magnetic inductance 750. Consequently, an upwardtraveling pulse of the magnetic inductance 750 acts as a pistontransferring generally upward momentum to the cathode particulates.

The cathode particulates support unidirectional electric current flowingthrough the electrolytic cell. Consequently, the cathode particulatesmust comprise electrically conductive or semiconductive materialsconsisting elements, metals, alloys, compounds, ceramics, organicpolymers, and inorganic polymers or combinations thereof. Theelectrolytic cell in accordance with the present invention utilizesplurality of particulates interacting with exposed surfaces of thecurrent feeder device 90. This allows for broad ranges of particulatesizes ranging generally from 0.1 mm to 10 mm of length in thecharacteristic dimension (possible characteristic dimensions include butare not limited to radius, diameter, ellipsoid axis, cylindrical radiusand axis).

The resistivity of the current carrying component of particulatessuitable for practical utility can range from about 1 nano ohmcentimeters to about 20,000 nano ohm centimeters. The cathodeparticulates can comprise common metals such as copper, aluminum, lead,nickel, iron, mild steel, stainless steel, zinc, titanium, silver, gold,platinum, palladium, tin, tungsten, carbon, and its mixtures andcombinations. Less common materials for the cathode particles such asconducting polymers, ceramics, semiconductors, and combinations ofsuitable substrate materials exhibiting appropriate conductivity wouldalso work with the present invention.

Products of electrochemical reactions associated with the properfunction of an electrolytic cell may accumulate in the cell andinterfere with long term cell functionality. Also, products ofelectrochemical reactions may be of commercial interest as produced orrepresent raw materials for further processing. The controlledaccumulation of products of electrochemical reactions can occur as anattachment and deposition on the cathode particulates, a sedimentedmaterial concentrated at lower parts of the cell chambers, or asincremental rise of concentration of materials dissolved in theelectrolyte or the presence of suspended product particulates.

FIG. 8 depicts several devices for controlled removal of products ofelectrochemical reactions from the cell. Products of electrochemicalreactions associated to the cathode particulates can be separated byextracting at least a portion of cathode particulates using separatingpipeline 800 controlled by removal valve system 810. The replacement ofthe cathode particulates is achieved via replacement valve system 820from the reservoir of fresh cathode particulates 830.

The separating pipeline 800 can be used to extract and separatesedimented products from the electrolyte and cathode particulates. Theproducts of electrochemical reactions dissolved in the electrolyte canbe removed using external pipeline 95 from the reservoir 97.

Processes of controlled removal of products of electrochemical reactionscan be performed continuously during the operation of the electrolyticcell as customary in the art of electrochemical disinfection orpollution removal, or using batch process as customary in art ofelectrowinning of metals. Both modes of operation are in accordance withthe present invention.

The direct current of constant intensity during the conduction like thecurrent profile 900 graphed in FIG. 9 is frequently the preferred choiceof current profile because of stability and simplicity of operation andassociated equipment. Other unidirectional current sources producingperiodic current profiles like profiles 920 and 930 also can be used ina device in accordance with this invention. The current profiles withtime dependences like 920 and 930 may provide advantages for specifictargeted applications such as selective product or product morphologycontrol. Aperiodic unidirectional currents like profile 910 in FIG. 9are frequently associated with programmable current sources operatingunder control of digital controllers.

DESCRIPTION OF PREFERRED EMBODIMENT

A brief overview of the proffered embodiment of the technology isincluded here. Over the course of relevant research a number ofadditional embodiments were conceived and explored. It is noted thatthis represents demonstration of technology function in the particularapplication and consequently is not optimal for many possibleapplications of the present invention.

A bench-scale version of the electrochemical apparatus was constructedand demonstrated. Here a simplified two-chamber cell is describedalthough stacked cell operation works also. Mirror image anode andcathode cell bodies were constructed from polycarbonate sheets to whichacrylic strips were welded to create the recesses of the cell chambers(Colorado Plastic Products Inc.). The cell chambers were sized to createan 8 inch by 10 inch active zone. The anode chamber active zone was inchdeep while the cathode chamber active zone was 1.5 inches deep and couldcontain about 2000 mL of cathode particles bed. When the anode andcathode cell bodies were clamped together while facing each other andsandwiching sealing foam strips and the separator membrane, a completedelectrolytic cell was formed. Electrolyte inlet and outlet ports werecreated as needed and were liquid tight electrical feedthroughs usingcommon polypropylene compression fittings (Cole Parmer). Two 4 inch×14inch EC-600 (Eltech Systems Corporation) anodes were mounted side byside in the anode chamber to create the anode. Spacers were added onboth anode sides to ensure free electrolyte access to the anode. Theanodes extended out the top of the cell allowing simple dry clamp typeelectrical contacts to be utilized. Two 4 inch×10 inch×0.0625 inch 316stainless steel plates (McMaster Carr) were mounted at the back of thecathode chamber to act as current distributors which define the activearea of the cell. Two ¼ inch dia. 316 stainless steel rods were mountedto each plate and passed through liquid tight feedthroughs to provideexternal electrical contact points suitable for simple dry clamp typeelectrical contacts to be utilized. Cut 302/304 stainless steel wire (2mm as cut, Pellets LLC) were used as the cathode particles bed. Standard1 inch dia.×13 inch Wood augers (Hickory Tools, Home Depot) were mountedin the cathode chamber to effect cathode particles bed churning. Theaugers were coated with polyurethane to prevent corrosion in thesynthetic acid mine drainage used for the electrowinning tests.Extenders were added to the augers so that they protruded out the top ofthe cell and gear and belt drive so that they could be easily rotated bya single external motor. A small variable speed DC gearmotor (2709K16,McMaster Carr) and a variable DC power supply (Extech 382213, Grainger)were used to rotate the augers and control the rotation speed (operatedin controlled voltage mode at 24 volts). A microporous ultra high weightpolyethylene membrane extending beyond the edges of the cell chambers(Gray Daramic-0.0097 inch thick, Polypore International Inc.) was usedto separate of the anode and cathode chambers when they were clampedtogether. The edges of the anode and cathode chamber were lined with acontinuous layer of ⅛ inch thick closed cell polyvinyl chloride foam(McMaster Carr) to create a gasket type seal when the cell bodies wereclamped together.

The electrochemical cell was operated in a batch mode utilizing arecirculating system for the electrolytes. For this demonstrative workthe electrolyte was shared so that both the anolyte and catholytecirculation were taken from and returned to the same single reservoir. A10 L volume of the standard solution was utilized for the batchoperation. The majority of the electrolyte was circulated through thecathode chamber using a larger peristaltic pump (Model 7533-80 with a7036-30 pump head, Barnant). A small portion of the electrolyte leakedinto the anolyte chamber and was recirculated using simple gravity feed.Similarly a portion of the electrolyte was circulated through a 1 cmpath length flow-through spectroscopic cell using a small peristalticpump (model 900-1445, Barnant) to allow near real-time monitoring of thesolution copper concentration. Filtering was used to remove any powderproduct generated which would impair the spectroscopic measurement. Thepumps were powered and their speed controlled using variable DC powersupplies (Extech 382213, Grainger) operating in the controlled voltagemode at 24 volts unless otherwise noted. All electrolyte circulationplumbing was either silicone, neoprene, polypropylene, or PVC whilereservoirs were Nalgene®—all of which are stable to the solutionemployed. The electrolyte temperature was measured using a Teflon coatedthermocouple (CASS-18G-12-PFA, Omega) while the pH was measured using agel filled double junction pH electrode (PHE-1411, Omega) and a signalpre-amp (PHTX-21, Omega). Selected operation and performance parameterswere monitored and digitally recorded each 10 seconds on a laptopcomputer using a analog to digital conversion data acquisition unit withmultiple channels (HP 34970A data acquisition unit with a 34901Amultiplexer module) and appropriate software (HP 34970A Data Logger 3).The copper concentration within the electrolyte was measuredspectroscopically at 840 nm using a Spectrophotometer 20+ (22348-108,VWR. The analog output of the spectrophotometer was recorded andconverted to copper concentration using a calibration curve preparedusing copper standards prepared with a 0.1 M sodium sulfate and 0.05 Msulfuric acid background. The electrolytic cell was energized with ahigh current variable DC power supply (Model XFR12-100, Xantrex)operated in the controlled current mode. The cell was operated at acurrent of 20 A.

The technology was successfully demonstrated for the improvedelectrowinning of copper from synthetic acid mine drainage. Thesynthetic acid mine drainage comprised an aqueous solution to whichcompounds were added to provide the proper pH, target electroactivespecies, and background ions to explore the chemistry of interest.Specifically the standard solution employed was prepared by adding 249.5g of copper sulfate pentahydrate, 142.1 g of sodium sulfate, and 500 mLof 1.0 M sulfuric acid to 9.5 L of water. This generated a syntheticacid mine drainage solution containing roughly 2000 ppm of cupric ions,0.182 M sulfate and 0.1 M sodium ions and provided 0.1 M of protons.Although the nominal pH of 0.1 M sulfuric acid is pH=1.0, buffering dueto the excess sulfate in the solution yields a pH of ˜1.6.

A stock solution with initial concentration slightly lower than thedesired 2000 ppm copper starting point, and roughly 6.5 L of electrolytewas used. The salient operating parameters are tabulated in Table 1while the observed performance is summarized in FIG. 10. The slope ofthe line in FIG. 10 indicates the copper removal rate. This dataillustrates that the apparatus works consistently down to very lowconcentrations, lower than 100 ppm.

TABLE 1 Electrolytic Apparatus Operating Conditions Parameter Value(s)Cell Power Current: 20 Amp Potential: 3.4-3.7 V Catholyte Pump Current:1.3 Amp Potential: 24 V Auger Drive Unit Current: 0.45 Amp Potential: 24V Copper Monitor Pump Current: 0.9 Amp Potential: 7 V Elcctrolyte Volume6.5 L Initial Copper Concentration 1609 ppm Final Copper Concentration38 ppm Treatment Time 3600 sec Electrolyte pH Initial: 1.6 Final: 1.5Electrolyte Temperature Initial: 21° C. Final: 25° C.

1. A method for electrochemical modification of liquid streams employingan electrolytic cell comprising steps of: a) providing at least oneelectrolytic cell for electrochemical modification of liquid streamswhich incorporates an anode, an anode compartment containing the anodeand a liquid electrolyte anolyte, a cathode compartment containing aliquid electrolyte catholyte and a cathode incorporating a plurality ofcathode particulates forming a cathode particulates bed, a currentfeeder device, a separator, a mechanical cathode particulates conveyancesystem arranged to manipulate motion of at least a portion of thecathode particulates via a direct mechanical interaction between themechanical cathode particulates conveyance system and the at least aportion of the cathode particulates, a system for circulation of theliquid streams through the electrolytic cell, and a system forconducting unidirectional electric current, b) circulating at least oneliquid stream undergoing modification through the at least oneelectrolytic cell, c) applying the mechanical cathode particulatesconveyance system to form the moving cathode particulates bed immersedin the catholyte and to transport the moving cathode particulatesthrough the catholyte substantially independently from the catholytecirculation, d) bringing the cathode particulates bed in at leastintermittent contact with the current feeder device, e) energizing thesystem for conducting unidirectional electric current to drive currentsupported by the at least one liquid stream from the anode through theanolyte and the separator and into the catholyte and to the cathodeparticulates and to the current feeder device during the contact betweenthe cathode particulates and the current feeder device, f) executingsteps b) through e) for the duration of time sufficient toelectrochemically react at least a predetermined quantity ofconstituents of the at least one liquid stream undergoing modification.2. The method of claim 1, wherein an additional step of adding asupporting solution to the at least one liquid stream is performedbefore the step b) in claim
 1. 3. The method of claim 1, where anadditional step of at least partial extraction and replacement ofcathode particulates and removal of the accrued products ofelectrochemical reactions from the cathode particulates is performedafter the step e) of the claim
 1. 4. The method of claim 1, wherein anadditional step of at least partial extraction from the electrolyticcell and removal from the electrolytic cell of sedimented products ofelectrochemical reactions is performed after the step e) of the claim 1.5. The method of claim 1, wherein an additional step of at least partialextraction from the electrolytic cell and removal from the electrolyticcell of products of electrochemical reactions dispersed in the liquidelectrolyte is performed after the step f) of the claim
 1. 6. The methodof claim 2, wherein the supporting solution is chosen from the set ofsolutions comprising liquid organic compounds, liquid inorganiccompounds, and mixtures of liquid organic compounds and liquid inorganiccompounds.
 7. The method of claim 2, wherein the supporting solution ischosen from the set of solutions comprising water, methanol, ethanol,all isomers of propanol, acetonitrile, carbon dioxide, ammonia,methylethyl ketone, tehydrofuran, dimethylsulfoxide, and mixtures andcombinations thereof.
 8. The method of claim 1, wherein the at least oneanode assembly incorporates at least one solid state geometricallystable anode.
 9. The method of claim 8, wherein the at least one solidstate geometrically stable anode comprises a conductive substratecombined with an oxidation catalyst.
 10. The method of claim 9, whereinthe at least one solid state geometrically stabile anode is chosen fromcommercial anodes consisting of a set of anodes that comprise platinizedtitanium, niobium coated copper, lead, lead alloy, and oxide coatedconductive substrate.
 11. The method of claim 1 wherein, the cathodeparticulates conveyance system that manipulates cathode particulatesmotion is an externally powered mechanical system that interacts withcathode particulates via direct mechanical interaction.
 12. The methodof claim 11, wherein the cathode particulates conveyance system thatmanipulates cathode particulates motion comprises at least one cathodeparticulates conveyor selected from the set consisting of a screw typeconveyor, a moving bucket type conveyor, a moving belt type conveyor,and a combination type conveyor incorporating any combination of thescrew, the moving bucket, or the moving belt.
 13. The method of claim11, wherein the cathode particulates conveyance system that manipulatescathode particulates motion a moving bucket type conveyor.
 14. Themethod of claim 1, where unidirectional electric current is variableunidirectional current of variable intensity during the conduction. 15.The method of claim 1, where unidirectional electric current is directcurrent of constant intensity during the conduction.